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Q.
Free RNA as infectious particle and of low molecular weight
NTA AbhyasNTA Abhyas 2020Biological Classification
Solution:
Viroids are the smallest infectious pathogens known, consisting solely of short strands of circular, single-stranded RNA without protein coats. They are mostly plant pathogens, some of which are of economical importance. Viroid genomes are extremely small in size, ranging from 246 to 467 nucleobases. In comparison, the genome of the smallest known viruses capable of causing an infection by themselves are around 2,000 nucleobases in size. The human pathogen hepatitis D virus is a defective RNA virus similar to viroids.
Viroids, the first known representatives of a new domain of "sub-viral pathogens," were discovered, initially characterized, and named by Theodor Otto Diener, plant pathologist at the U.S Department of Agriculture's Research Center in Beltsville, Maryland, in 1971. The first viroid to be identified was Potato spindle tuber viroid (PSTVd). Some 33 species have been identified.